Violent storms in the U.S. are being blamed for the deaths of at least 13 people and widespread power outages as more than 3 million people in the the eastern U.S. are facing temperatures in the 40s without electricity, and without air conditioning.

Six people were reported killed in Virginia, including a 90-year-old woman asleep in bed when a tree slammed into her home. Two young cousins in New Jersey were killed when a tree fell on their tent while camping. Other deaths were reported in Maryland, Ohio, Kentucky, and Washington, D.C.

Washington and other areas were still largely without power. People chose to escape the heat in shopping malls or hotels. Drivers navigated through intersections left unguided by dead traffic lights.

In suburban Washington, emergency call centres were without power and residents were told to go to police or fire stations if they needed help.

Golfers walk down the fairway at the AT&T National golf tournament in Bethesda, Md., Saturday, where spectators were not allowed after a storm damaged the course. (Patrick Semansky/Associated Press)

In addition to the heat, officials say cell phone coverage is spotty. Many residents were asked to conserve water because sewage stations had been without power for a time. And authorities cautioned people to drive carefully because tree limbs littered roads and hundreds of traffic signals were out.

West Virginia Gov. Earl Ray Tomblin declared a state of emergency after more than 500,000 customers in 27 counties were left without electricity.

Winds uprooted trees at the AT&T National golf tournament in Maryland, leading officials to take the rare step of closing the course to spectators and volunteers for safety reasons. However, play was expected to continue.

At least four utility poles fell on a road in Columbus, Ohio, making it too dangerous for people in four cars to get out, police said. One person was taken to a hospital.

As of 9:30 a.m. ET Saturday, Pepco was reporting 440,000 outages in the District of Columbia and Montgomery and Prince George's counties, Md. Washington radio station WTOP was reporting a much higher number.

"We have more than half our system down," said Pepco spokeswoman Myra Oppel. "This is definitely going to be a multi-day outage."

Pepco spokesman Clay Anderson told CBC News it will take several days to restore power to all customers in the Washington area.

Amtrak passengers stranded

A storm that knocked down trees across several states stranded 232 Amtrak passengers overnight on a train in West Virginia.

Amtrak spokesman Steve Kulm says all the passengers have been loaded onto buses that will ferry them to their eventual destination. The buses departed by 8:20 p.m. Saturday.

The riders aboard a train from New York to Chicago had been stranded near the town of Prince since about 11 p.m. Friday because fallen trees were blocking the tracks in front of the train and behind it.

Kulm says the train had power, lights and air conditioning. Passengers could get in and out because they were parked at a station. The train was also stocked with food. The stranded train was first reported by the transportation blog Jalopnik.

The U.S. National Weather Service warned temperatures could climb near or above 40 C on Saturday in many areas that were already without power. Thousands were without electricity in their homes and were seeking refuge in movie theaters, shopping malls, restaurants and official cooling centres. Forecasters warned that another round of storms was possible in the afternoon, which could complicate cleanup efforts.

Jose Amaya, 41, of Germantown, Md., said his wife and two daughters planned to hang out at the mall to stay cool and he joked that the outage was going to cost him because they would be shopping. His wife, who works for a hotel chain, also planned to get the family a room to stay.

In the U.S. capital, the Metrorail subway trains were returned to their endpoints due to the storms and related damage, officials said.

"It has had a widespread effect on the region," Metro spokesman Dan Stessel said early Saturday. He said about 17 train stations were operating on backup power due to local power outages, but that he didn't anticipate service being disrupted on Saturday.

Amtrak suspended its service from Washington, D.C., to Philadelphia due to the storms, at least until mid-morning.

More than 20 elderly residents at an apartment home in Indianapolis were displaced when the facility lost power due to a downed tree. Most were bused to a Red Cross facility to spend the night, and others who depend on oxygen assistance were given other accommodations, the fire department said.

About 418,000 were without power in Baltimore County, Md.; 1.25 million customers in Virginia, including the suburbs outside Washington; 419,000 in Washington, D.C.; 800,000 to 1 million in Ohio; 500,000 in West Virginia; and 170,000 in New Jersey.

The storms hit as cities along the coast sweltered in record-setting heat.

Earlier Friday, the nation's capital reached 40 C, topping a record of 38 C set in 1934.